1. Field of the Invention
The invention relates to a method for adapting a clutch.
2. Description of the Related Art
Vehicles with a parallel hybrid drive have an internal combustion engine and an electric motor arranged on one shaft in the drive train. Either the internal combustion engine or the electric motor or both machines can be used to drive the vehicle. A clutch is provided between the internal combustion engine and the electric motor. The clutch is disengaged in a purely electrical driving mode so that the internal combustion engine can be switched off and the vehicle can be driven by the electric motor. Engagement of the clutch enables the internal combustion engine to transmit a torque to the drive train and drive it. This can take place with a driving electric motor or with a freely rotating electric motor.
The connection of the internal combustion engine following pure electric operation should not be perceived as disruptive to passengers in the vehicle. For example, the connection of the internal combustion engine should not result in a jolt caused by suddenly increased torques or suddenly reduced torques. The connection only starts as a result of the tow starting of the internal combustion engine. Thus, a portion of the torque available for the propulsion would be branched off suddenly and used for tow starting the internal combustion engine. This reduction in torque for propulsion would be perceptible even in the case of only partially closing the clutch unless there is an additional increase in torque. An additional torque could be made available by the electric motor. However, the closing of the clutch must be controlled so that the actual additional torque is used only for the tow starting of the internal combustion engine and therefore no jolt occurs.
The torque that can be transmitted by the clutch is determined by a clutch characteristic curve. The characteristic curve can be shifted or distorted during operation due to thermal changes and mechanical tolerances. Therefore, a resulting transmissible torque when the clutch is engaged may not correspond to the expected transmissible torque. Jolts may be experienced when the internal combustion engine is tow started if the torque transmitted by the clutch does not correspond to the intended transmissible torque. The clutch position itself typically is not detected, but instead a position of the master cylinder of the actuator or some other position of the actuator is detected. As a result, a difference can occur between the actuator position and the actual clutch position. This difference may be caused, for example, by thermal effects. The thermal shifting causes the clutch position that occurs to differ from the clutch position that is expected.
For this reason, an ability to detect or determine as precisely as possible the torque that can be transmitted by the clutch is of decisive importance for the quality of the connection of the internal combustion engine in vehicles with a parallel hybrid drive.
The object of the invention is to provide a method for adapting the torque that can be transmitted by the clutch and that permits the torque that can be transmitted by the clutch to be determined precisely despite thermal changes or other tolerances are present.